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RISSOIDAE


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Rissoina (Rissoina) angasi Pease, 1872

Description: Shell tall and slender, with spire weakly convex. Protoconch of 1 whorl, with distinct junction with teleoconch. Teleoconch of 5-7 weakly convex whorls, strongly angled at top of all whorls. Whorls sculptured with strong axial ribs, without spiral sculpture. Last whorl with very strong, nodulose spiral rib on base with a wide, deep groove above. Aperture lens or D-shaped, with broad anterior canal and narrow posterior canal; outer lip expanded, not thickened internally, with strong varix externally; inner lip callused, thickened at top and bottom. Colour uniformly white, translucent when fresh, becoming opaque with age.

Size: Up to 7.3 mm in length

Distribution: Endemic to Australia; The Entrance, NSW, southwards and around southern Australia including Tasmania, and then northwards on the Western Australian coast to Onslow, WA.

Habitat: Most specimens are empty shells from beach washup, but there are subtidal records down to 150 m. Common.

Comparison: This is very similar to Rissoina crassa, but is tall and slender, and all whorls are angled at the top. It is also similar to R. decipiens, but has a different protoconch and lacks the fine spiral threads on early whorls found in that species.

Synonymy: None.

Fig. 1: Shell Harbour, NSW (C.323542)

 

Copyright Des Beechey 2010